This year, two major scientific issues requiring international co-operation hit the headlines. One was climate change, which was in the news with the publication of the long-awaited Fifth Assessment Report, known among the cognoscenti as AR5. The other was the outbreak of the Ebola virus in western Africa.

Climate change and a deadly epidemic may seem to have little in common. The former is slow but inexorable; the latter is likely to peak and recede rapidly. But, interestingly, they present similar challenges: neither respects borders or nationality; both require international collaboration if they are to be effectively dealt with; and poorer countries are likely to suffer a disproportionate burden. In both cases, the media can swing from indifference to alarm, leaving us confused about where the truth lies. And in both cases, national responses to these two issues require drawing upon highly specialised scientific knowledge.

This year’s multi-volume climate change report is the latest in a series starting in 1990 and produced by the Intergovernmental Panel on Climate Change (IPCC). The panel is a global initiative, created to assess the science related to climate change and present it for those who are interested. It does not do research itself, but instead analyses existing scientific publications and synthesises its reports from them. The reports are written by more than 200 scientists from 39 countries, who volunteer their time and expertise to scrutinise the latest scientific findings.

Given the global significance of climate change and attempts to ameliorate it, the reports are required reading in government and environmental circles.

The four tomes that comprise the new AR5 have been several years in the making. The first of them (the Physical Science Basis) actually appeared at the end of 2013. The rest (Impacts, Adaptation and Vulnerability, and Mitigation) followed during the course of 2014.

The previous Assessment Report (AR4) was released in 2007, and has been perused and quoted regularly since. AR4 had its share of controversy and a few errors (for instance, what turned out to be an exaggerated claim about glacial melting in the Himalayas, which was later retracted), but its central message about the progressive nature of human-caused climate change was unflinching, and backed by enormous scholarship.

Since that time, the science has continued to move forward, and there was eager anticipation of what the new report would say. In measured and careful text, it presents a sobering series of facts and projections, concluding that it is now more certain than ever that human civilisation is the main cause of global warming. It finds that each of the last three decades has been warmer than any preceding decade since 1850. Combined land and ocean temperatures rose on average by 0.85oC since 1880. From 1901 to 2010, the sea level rose by 19cm—more quickly than the average for the last 2000 years. Greenhouse gases in the atmosphere, from fossil fuels and changes to land use, have reached concentrations unseen in at least 800,000 years. A third of the additional carbon dioxide added by human activity has been absorbed by the oceans, making them more acidic.

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What is unequivocal is that ’the atmosphere and ocean have warmed, the amount of snow and ice has diminished, the global mean sea level has risen and the concentrations of greenhouse gases have increased,’ as Dr Qin Dahe, co-chair of the IPCC working group that compiled the report, expressed it.

The changed temperatures not only make heatwaves more frequent, but can also cause a range of creatures to slowly shift location. This can have serious implications for human diseases. Various species of mosquito and other vector insects that carry diseases are gradually expanding the area in which they can survive. One of the pioneers in

the field of the health effects of climate change, Australian epidemiologist Professor Tony McMichael, died this year. But his legacy lives on, with a vibrant field of research continuing. Much of this research suggests that global warming will expose more of the world’s population to a greater range of diseases, as well as to direct effects of higher temperatures on people. At the same time, of course there will be fewer cold-related deaths, but some evidence so far suggests that the increased deaths from warming could outweigh the reduction in cold-related mortality. More work is underway to get a clearer picture of the potential health effects of climate change.

Of course, it would be incorrect to blame climate change for this year’s outbreak of Ebola. They are not connected. But the similarity lies in the fact that environmental issues and human health are often related, and that global responses may be required. Ebola is not a human virus. It is an example of a zoonosis, an animal disease that is incidentally able to infect humans and has managed to move across to us. Evidence suggests that the natural hosts are bats and other forest-dwelling mammals, and that the first known case in this outbreak (there have been several other past outbreaks) came from a family that had hunted bats. As the human population in Africa expands and forests are fragmented, it is thought that more people come into closer contact with infected forest animals. Humans and infected animals interact, as people hunt the remaining ‘bush meat’ or as forest animals in search of food leave a degraded habitat to move closer to human settlements. Ebola is an example of an ‘emerging disease’, and there are plenty more. About 300 such diseases have been notified since 1940, of which more than 60% are zoonotic in origin. SARS (Severe Acute Respiratory Syndrome) and MERS (Middle Eastern Respiratory Syndrome) are other global examples, and in Australia we have Hendra virus.

Dealing with a contagious and deadly pathogen like the Ebola virus, for which there is as yet neither vaccine nor proven cure, calls for a global agency, and the World Health Organisation (WHO) is the body responsible. When confronted with the prospect of the disease, each country wishes to protect itself, but needs to co-operate with others in order to do so. Climate change has provided the human race with a similar challenge. Eliminating emissions from an individual country such as Australia (responsible for about 1.5% of the world’s greenhouse gases) will not stop climate change. No single country’s emissions are solely responsible for the problem. Only collective action is likely to be fully effective.